Such a valve operating system is conventionally known, for example, from PCT International Patent Application Laid-open No.WO95/00959 and the like.
In the valve operating system disclosed in the above PCT Internationial Patent Application, the armature is fixed to the upper end of the stem of the engine valve, and in order to provide a reliable seated state of the engine valve, even if an elongation of the stem is produced due to the thermal expansion, a gap is created between the valve-closing electromagnet and the armature in the seated state of the engine valve.
However, the seating force for the engine valve on the valve seat member depends on the electromagnetic force of the valve-closing electromagnet, and the seating force is varied substantially by a variation in the electromagnetic force due to a variation in value of a current supplied to energize the valve-closing electromnagnet.
The present invention has been accomplished with such circumstances in view, and it is an object of the present invention to provide a valve operating system in an internal combustion engine wherein a stable seating force for the engine valve is provided irrespective of the elongation of the stem and the variation in current supplied to the valve-closing electromagnet.
To achieve the above object, according to the present invention, the valve-operating system is constructed so that only the resilient force of the valve-closing resilient means is applied to the engine valve when the engine valve is seated on the valve seat member. Thus, the seating force for the engine valve is determined by the resilient force of the valve-closing resilient means and hence, a stable seating force can be provided.
According to the present invention, the resilient force of the valve-opening resilient means is applied to the armature to stop the application of the resilient force to the engine valve with attraction of the armature toward the valve-closing electromagnet, and the resilient force of the valve-closing resilient means is applied to the stem which is capable of being axially moved relative to the armature during attraction of the armature toward the valve-closing electromagnet. Thus, only the resilient force of the valve-closing resilient means is applied to the stem of the engine valve with attraction of the armature toward the valve-closing electromagnet by the energization of the valve-closing electromagnet. Therefore, the seating force for the engine valve can be determined by the resilient force of the valve-closing resilient means without the need for a complicated control.
According to the present invention, the armature and the stem are operatively interconnected through a connecting means which is adapted to enable the armature and the stem to be moved in unison with each other during closing of the engine valve, until the engine valve is seated on the valve seat member, but to permit the armature to be moved toward the valve-closing electromagnet in the axial movement relative to the stem after stoppage of the movement of the stem as a result of seating of the engine valve. Therefore, after seating of the engine valve, the armature can be moved toward the valve-closing electromagnet with the stem remaining in the valve-seated position, and the transmission of the force from the armature can be cut off from the engine valve, so that the seating force can be provided by only the resilient force of the valve-closing resilient means applied to the stem.
Further, according to the present invention, the connecting means includes a bottomed cylindrical cap which is fixed to an upper end of the stem, so that it can be engaged with the armature from the side opposite from the valve-closing electromagnet and which is fitted into the armature for axial relative sliding movement. Therefore, the outer peripheral surface of the cap can be easily formed as a slide surface by machining.
Still further, according to the present invention, the connecting means includes a bottomed cylindrical cap which is formed into a bottomed cylinder-like configuration and fixed to the armature and into which an upper portion of the stem is slidably fitted. Therefore, the cap and the armature are in a state in which they are supported by the upper portion of the stem during movement of the armature toward the valve-closing electromagnet, and hence, it is possible to prevent the deflection of the armature to stably attract the armature to the valve-closing electromagnet.
Furthermore, according to the present invention, the cap has an opened bore in its closed end. Therefore, it is possible to avoid the pressurization and depressurization of a space created between the cap and the stem slidably fitted in the cap, and to prevent the stem from being attracted upwards when the volume of the space is increased during closing of the engine valve, thereby preventing an increase in seating force.
Also according to the present invention, the distance through which the armature is moved toward the valve-closing electromagnet after seating of the engine valve is set at a value equal to or larger than the maximum amount of elongation of the stem due to the thermal expansion of the engine valve. Therefore, it is possible to cope with the thermal expansion of the engine valve to ensure the normal operation of the engine valve at an increased temperature.